This invention relates generally to storage and retrieval systems, and more particularly, to a storage and retrieval system having a flexible drive arrangement for loading and unloading articles such as tote bins stored in respective compartments of a matrix arrangement of such compartments; the load/unload drive arrangement having a flexible drive loop arranged to move along a predetermined drive path which is disposed centrally with respect to the articles, and a latching push and pull member for permitting pulling of a tote bin from a compartment or pushing a tote bin into a compartment which is misaligned during the replacement phase of operation.
Storage and retrieval systems are generally known to consist of a plurality of compartments forming a two-dimensional matrix for storing articles and a mechanized arrangement, which may be a stacker crane, for removing a selected article from its compartment, and loading the article onto a transfer carriage so that it may be conveyed to a predetermined location; which location may be a utilization area for the article, an order inventorying station with a human operator, or another compartment. After the desired manipulation of the article has been performed, the mechanism on the transfer carriage can reinsert an article into a compartment. In several known storage and retrieval systems, the compartments are arranged in the form of a two-dimensional matrix having a plurality of rows and columns and open ends in a single plane. Additionally, a second matrix of compartments may be arranged parallel to the first matrix thereby creating an aisle therebetweeen. A stacker crane moves horizontally along the aisle and transports a transfer carriage vertically, such that the transfer carriage and its attendant mechanisms remove and replace articles from at least the first matrix of compartments, and in facilities where there is a plurality of matrices, inter-matrix transfer of articles may be performed.
It is generally preferred that the articles have certain uniform characteristics and dimensions so that the storage and retrieval processes are facilitated. Such uniformity between the articles has been achieved by placing the particular goods which are being warehoused in tote bins which are specifically adapted for use in a storage and retrieval system. Of course, the commodities which may be stored in the various bins come in a variety of sizes. Thus, it is desirable that the tote bins be configured to have at least one dimension which is commensurate with the dimensions of the commodity stored therein, all within the context of maintaining a high storage density for the overall facility. In other words, the commodities should be stored in the smallest tote bins which will accomodate them, and all such tote bins should be arranged in one matrix of compartments such that the adjacent aisle need be only wide enough to accommodate the tote bins and the required transfer carriage and mechanisms.
It is well established in the industry that there exists the need for systems which can access and retrieve articles stored in a matrix of compartments while also providing high storage density. In some commonly used equipment, a variety of limiting characteristics are present in the design of the equipment which adversely effects storage density.
Several of the characteristic limitations inherent in known storage and retrieval equipment are evident in the structure described in U.S. Pat. No. 3,802,580 to Castaldi. This reference described an inventory storage system wherein an arm enters a selected compartment and penetrates to engage behind the rearmost article arranged therein. Outward travel of the arm with its engagement apparatus deployed moves all of the articles in a direction outward of the compartment until a preselected number of articles are deposited onto a platform. The engagement apparatus is then disengaged, and the arm is withdrawn from the compartment. First, it is evident that there must be sufficient space provided in each compartment for all of the articles stored therein and sufficient space must remain for the arm to penetrate into the compartment. Clearly, such a compartment must be substantially larger than is necessary to accomodate the articles stored therein, thereby limiting the overall storage density of the system. It is further evident from this known structure that the arm must extend into the compartment for a depth sufficient to permit the engagement apparatus to be deployed on the inward side of the innermost article. Clearly, as such an arm is withdrawn from the compartment, the width of the aisle between consecutive, facing compartment matrices must be sufficiently large to accomodate the arm transversely therein. Since the arm must be even longer than the depth of the compartment, such that it may be supported at the platform while it is extended, the large minimum required width of the aisle severely reduces overall storage capacity and density in the facility.
There is, therefore, a need for a storage and retrieval system which does not require penetration into the compartment by an arm, and it is accordingly one object of this invention to provide such a system.
A known warehouse crane which is subject to the limitation just mentioned is described in U.S. Pat. No. 4,358,293 to Dechantsreiter. The known arrangement which is the subject of this patent reference is provided with a pair of rotatable chain loops extending horizontally along a transfer carriage of fixed length; the four chain loop extending parallel to the direction of travel of a tote bin which is desired to be conveyed. The length of this transfer carriage is fixed for use in facilities wherein the aisles are of uniform width. The designers of the known structure, however, recognized the need for moving the transfer carriage transversely within an aisle, and therefore provided a mechanism by which the transfer carriage is moved, over a limited range, with respect to its support beams.
It is a problem with this known tote bin storage system, and others, that a tote bin which is desired to be inserted at a storage compartment may jam during insertion as a result of misalignment, thereby requiring manual realignment to perform the storage procedure. This results from the fact that generally a tote bin is inserted into its storage compartment by operation of a push member which is not otherwise secured to the tote bin. Thus, the push member can not be utilized to withdraw a jammed tote bin outwardly from the compartment. This problem is compounded by the fact that a jammed tote bin is out of position for engaging with the pull member, thereby requiring the jammed tote bin to be cleared manually. Moreover, such systems engage with the tote bins off center, thereby causing the misalignment of the tote to persist.
The inability of the known storage and retrieval systems to correct a jammed tote bin situation without human intervention is evident in U.S. Pat. No. 4,352,622 to Weischel. Weischel describes an article transfer arrangement wherein counter-rotating chains are provided on respective sides of a transfer carriage. The counter-rotating chains are each provided with a push member and a pull member which communicate with respective push and pull surfaces of a tote bin. This known arrangement is provided with a push member which does not engage with the tote bin except for the communication with the push surface thereof. Thus, in the event that a tote bin should become jammed as a result of a misalignment during the insertion procedure, manual intervention is required to effect correction. Correction of the jammed tote bin situation can not be achieved by reversing the drive of the chains because the push member will simply move away from the tote bin, and the tote bin is out of position for engagement with the pull members.
It is therefore, yet a further object of this invention to provide an article transfer arrangement wherein tote bins which become jammed during the storing procedure can be withdrawn outwardly of the compartment without manipulation by a human operator.